Molds are known, in particular injection molds, that are made of a plurality of blocks that define a mold cavity when they are in an assembled position. Such molds are normally used for injection molding, e.g. for injection molding turbine engine blades. The closed mold cavity defines the shape of the part to be molded. Injection is often performed at high temperature, in which case the temperature of the mold is reduced at the end of injection in order to unmold the part under good conditions without harming its properties. Nevertheless, since the part and the blocks of the mold are made of different materials (e.g. blocks made of metal and part made of carbon) differential expansion occurs that may have the effect of jamming the part in the mold.
Furthermore, when the mold cavity is opened by separating at least one block of the mold from the remainder of the mold, the part is subjected to cooling that is non-uniform as a result of the temperature difference between the air in the workshop that is in contact with a portion of the part, and the remaining block of the mold that are in contact with another portion of the part. This temperature gradient gives rise to residual stresses in the part. These residual stresses increase with increasing length of the time taken to perform unmolding. It is therefore necessary to provide special methods or appropriate tools for unjamming and extracting the part quickly from the mold.
A known solution to the problem of unmolding consists in providing a mold made up of numerous blocks, and in removing the blocks one by one until the part is completely disengaged. Such a solution is lengthy to perform and generally requires the mold to be handled (rotated, turned upside-down, tilted, etc.), and this can be found to be complex once the mold exceeds a certain size or its temperature is relatively high.
Another known solution consists in using an external tool for applying a force on the part and for separating it from the mold, e.g. wedges or a crowbar. However, the force that needs to be exerted is relatively large and such a technique often damages the molded part, in particular by leaving marks on the part.
An improvement to that problem consists in leaving a narrow through hole in a block of the mold, the through hole then connecting the mold cavity to the outside of the mold. The hole is plugged temporarily before and during molding, generally by means of a screw and a resin of the room temperature vulcanization (RTV) silicone type. At the end of injection, the mold is opened by separating at least one block of the mold from the remainder of the mold, the RTV resin is removed, and a rod is inserted in the through hole from the outside in order to exert a force on the part so as to separate it from the mold. Nevertheless, that method suffers from the above-mentioned drawbacks concerning the use of an external tool. Furthermore, the sealing provided by the RTV resin is of limited reliability and it can happen that the material injected into the mold pushes back the resin and escapes via the through hole during molding. Such a solution is thus not satisfactory. There therefore exists a need for a novel type of mold.